The present invention relates to a nozzle unit in a paper machine or finishing machine for paper. The nozzle unit is arranged to cut the processed paper web in connection with a reel change when the change takes place substantially at the normal running speed of the machine, such as in so-called Pope-type reelers and reel-ups developed from Pope-type reelers. The nozzle unit according to the invention can also be used In two-drum winders and in connection with threading in all reel-up types.
Publication EP 0543788 discloses a waterjet cutting apparatus in which a pressure of 400 to 600 bar is used. FIG. 1 in the publication shows a supporting structure, in which the nobles are arranged to move in the cross direction of the web The nozzles are connected to a control and adjustment unit that can also comprise a water container.
Publication U.S. Pat. No. 4,695,004 discloses a waterjet cutting apparatus, in which the cutting nozzles are connected to a stationary high-pressure pump by means of a flexible hose,
Publication FI 99283 and the corresponding U.S. Pat. No. 5,842,664 disclose a method for cutting a wedge-shaped end during threading in a reeling device of a web-like material, such as a slitter winder.
Publication U.S. Pat. No. 3,877,334 discloses a method and an apparatus for cutting sheet material with a fluid jet. The apparatus comprises a pressure amplifier, which has small and large area pistons, and includes a fluid reservoir for a cutting fluid. A pressurizing fluid, which is led through a hydraulic conduit, energizes the cutting fluid.
In a paper machine the change of the reel spool must be conducted successfully at the same time when the paper web is run at a speed which is at least 1500 m/min. The change refers to the event in which the paper web guided on a paper reel that is becoming full is changed to be reeled around a new, empty reel spool. Because the change takes place at high speed, substantially at the normal running speed, this makes high demands on the cutting of the paper web in connection with the change of the reel spool. The paper web must be cut rapidly, because the length of the waste paper produced in the cutting is determined by the relation of the running speed with the cutting speed. When the paper web Is cut as the web is moving at the running speed and the cutting member is moving in the cross-direction of the paper web, a wedge is produced in the cutting, which wedge should form an angle not larger than 45° with the cross-direction of the paper web, because otherwise too large an amount of waste paper is produced and the new paper reel starts to bend during reeling in such a manner that a clear protrusion occurs in the paper reel reeled on the reel spool. It has to be possible to accelerate the cutting end rapidly.
Generally cutting by means of liquid, typically waterjet cutting, is implemented with a pressure of 300 to 1000 bar. Problems are caused by the solid structures required by the high-pressure cutting, which are difficult to move. Moving is difficult, because the high-pressure hoses are stiff and require large bending radii. When lighter structures are used, there is a danger that the connectors may leak and the hoses may break. In waterjet cutting, problems are also caused by the eroding effect of water, wherein both the nozzle and the pressure pump wear rapidly.